1. Field of the Invention
The present invention relates to an ink ribbon winding mechanism, and in particular to an ink ribbon winding mechanism suitable for winding a multi-colored ink ribbon, on which inks of different colors are applied, and detecting correctly markers for color identification formed in the ink ribbon.
2. DESCRIPTION OF THE PRIOR ART
Prior art printers are so constructed that desired printing is effected, in general, by transferring the ink applied on the ink ribbon to a sheet of paper by means of a printing head having a printing element consisting of a plurality of dots.
FIG. 7 shows a prior art printer of this kind generally utilized. A plate-shaped platen 2 is so disposed nearly at the central portion of a frame 1 of the printer that the printing face thereof is approximately vertical and a carriage shaft 3 is disposed so as to be parallel to the platen 2 stated above downward before the platen 2 of the frame 1 described above. Further, there is formed a flange-shaped guide portion 4 at the front edge of the frame 1 and a carriage 5 is mounted movably forward and backward along the carriage shaft 3 and the guide portion 4 on the carriage shaft 3 and the guide portion 4. A printing head 6 is mounted on the extremity of the carriage 5 so as to be opposite to the platen 2 described above and a ribbon cassette (not shown in the figure) is mounted, in which the ink ribbon is located and which guides this ink ribbon between the printing head 6 and the platen 2.
Further, on the carriage 5, there is disposed a winding mechanism 7. As indicated in FIGS. 8 and 9, this winding mechanism 7 has a winding shaft 8. On the lower end portion of this winding shaft 8, a supporting flange 9 protruding outward is formed in one body, and at the same time the shaft is inserted in a winding gear 10, which is mounted rotatably, independently of the winding shaft 8 described above. Still further, a piece of felt 11 acting as a slipping mechanism is disposed between the lower surface of the winding gear 10 and the supporting flange 9 of the winding shaft 8. To the upper end portion of the winding shaft 8, there is secured a winding bobbin 12 engaged with a winding hole (both not shown in the figure) formed in the ribbon cassette, exposed on the upper surface of the carriage 5. On the outer peripheral surface of this winding bobbin 12, there are formed 3 engaging nails 13 at positions driving equally the periphery into 3 so as to protrude therefrom and on the lower surface of the winding bobbin 12, there is formed a ring-shaped holding groove 14. An energizing spring 15 is disposed on the outer periphery of the winding shaft 8, whose upper end portion is held in the holding groove 14 formed in the winding bobbin 12 and whose lower end portion is contacted with the upper surface of the winding gear described above so that the winding gear 10 is contacted with the supporting flange 9 of the winding shaft 8 through the piece of felt 11 described above with pressure owing to the energizing force of this energizing spring 15.
Still further, a driving gear 18 secured to the rotating shaft 17 of a ribbon winding motor 16 is engaged with the winding gear 10 so that the driving gear 18 is rotated by driving to rotate the ribbon winding motor 16 and thus the winding gear 10 is rotated. In this way, this rotational driving force is transmitted to the winding shaft 8 through the frictional force of the piece of felt 11 produced by the energizing force of the energizing spring 15 mounted on the winding gear 10.
Still further, behind the platen 2 stated above, there is formed a sheet insertion opening 19 for forwarding a sheet of paper (not shown in the figure) towards the platen 2, and in the proximity of the sheet insertion opening 19, there is disposed a sheet forwarding roller 20 for forwarding the sheet of paper with a predetermined speed. Under this sheet forwarding roller 20, there is disposed rotatably a with-pressure-contacted roller 21 contacted with pressure with this sheet forwarding roller 20 so that the sheet of paper inserted through the sheet insertion opening 19 is put between the sheet forwarding roller 20 and the with-pressure-contacted roller 21 to be forwarded.
In the prior art printer described above, the sheet of paper is inserted through the sheet insertion opening 19 so as to be put between the sheet forwarding roller 20 and the with-pressure-contacted roller 21 and forwarded with the predetermined speed in the direction perpendicular to the movement direction of the carriage 5 by driving the sheet forwarding roller 20 so as to be rotated by means of the stepping motor. On the other hand, the ribbon winding motor 16 is driven at the same time as the drive of the carriage 5 described above and the winding shaft 8 is rotated through the winding gear 10. In this way, desired printing is effected on the sheet of paper by driving the printing head 6 on the basis of desired printing signals while winding the ink ribbon by rotating the winding bobbin 12.
Further, in the case where a multi-colored ink ribbon, on which inks of a plurality of colors are applied, is used as the ink ribbon located in the ribbon cassette stated above, either as indicated in FIG. 10(a), there are disposed markers 23 having different sizes in the longitudinal direction for different colors at boundary portions of the different colors, which are e.g. yellow (Y), magenta (M) and cyan (C), on the ink ribbon 22, or as indicated in FIG. 10(b), there are disposed markers 23 having numbers of lines different for different colors at the boundary portions of the different colors. When it is desired to detect the different colors in this ink ribbon 22, the different colors are detected by reading out the markers stated above while winding the ink, ribbon by driving the ribbon winding motor 16 to rotate the winding bobbin 12, just as at winding the ink ribbon, neither the carriage 5 nor the printing head 6 being driven.
However, in the prior art ink ribbon winding mechanism described above, in the case where the colors of the multi-colored ink ribbon are detected, the winding shaft 8 is rotated through the winding gear 10 and the piece of felt 11, if the load at the winding of the ink ribbon exceeds the frictional force produced when the winding gear 10 is contacted with pressure with the supporting flange 9 by means of the energizing spring 15, sliding takes place between the winding gear 10 and the winding shaft 8 and therefore it has a problem that fluctuations are produced in the rotation of the winding shaft 8. Because of these fluctuations in the rotation of the winding shaft 8, since the displacement speed of the markers in the ink ribbon is varied, it has another problem that it is impossible to detect the markers, or erroneous colors are detected.